Clinical value of M22-based assays for TSH-receptor antibody (TRAb) in the follow-up of antithyroid drug treated Graves' disease: Comparison with the second generation human TRAb assay

BackgroundWe compared the clinical performances of two new M22-based assays for TSH-receptor antibody (TRAb) with those of the human TRAb assay (hTRAK) in Graves' disease patients at the end of treatment.Patients and methodsSera were obtained from 128 Graves' patients treated for 18 months with antithyroid drugs. Sixty-six remained in remission and sixty-two had relapse of hyperthyroidism in a 3-year follow-up after discontinuing treatment. TRAbs were measured using two M22-based methods (electrochemiluminescence using the Cobas® or ELISA using the Medizym® TRAb clone) and with the hTRAK.ResultsAt T18, the results were significantly higher by the Cobas® assay (median: 2.7 IU/L, range: 1.1–18.5 IU/L) or lower by ELISA (median: 0.56 IU/L, range: 0.22–14.8 IU/L) than those obtained for the hTRAK (median: 1.5 IU/L, range: 0.9–9.8 IU/L). The use of cut-off limits at 1.9 IU/L, 3.2 IU/L and 0.94 IU/L gave similar and higher prevalences of TRAb-positive patients in the group of relapse as compared to the remission group. However, some patients remained misclassified in each remission or relapse group.ConclusionsThe M22-based TRAb assays did not improve the predictive value of relapse obtained with the hTRAK measured at the end of treatment. High inter-method variability requires assay harmonization for correct interpretation of results.